Save image from url in django and checking if it´s an image

I have the following code in a view:

from django.core.files.temp import NamedTemporaryFile

...

image_url = request.POST['url']
name = urlparse(image_url).path.split('/')[-1]
picture = Picture()
picture.user = request.user     
img_temp = NamedTemporaryFile(delete=True)
img_temp.write(urllib2.urlopen(image_url).read())
img_temp.flush()
picture.picture.save(name,开发者_运维技巧 File(img_temp))
picture.save()

which works fine, but I want to make sure the "img_temp" is actually an image. How can I achieve this?

EDIT:

I´ve found a solution. Theres a module in python called imghdr that makes byte-level verification to files to see if they are images. It can be used like this:

from django.core.files.temp import NamedTemporaryFile
import imghdr

    image_url = request.POST['url']
    name = urlparse(image_url).path.split('/')[-1]
    picture = Picture()
    picture.user = request.user     
    img_temp = NamedTemporaryFile(delete=True)
    img_temp.write(urllib2.urlopen(image_url).read())
    img_temp.flush()        
    to_save = File(img_temp)
    to_save.open()
    extension = imghdr.what(to_save)
    if not extension in ['jpg', 'jpeg', 'png', 'gif']:
        to_save.close()
        return None
    picture.picture.save(name, to_save)
    foto.save()

Please let me know if you see any bugs in this code.

img_temp = NamedTemporaryFile(delete=True)

--> it does not work in Django 1.3, instead use:

img_temp = NamedTemporaryFile()

this line of code waste me 2hours

Why don't you just validate to see if image_url is an image?